U.S. patent application number 11/370462 was filed with the patent office on 2006-07-06 for organic semiconductor devices and organic electroluminescent devices produced by using wet process.
Invention is credited to Byoung-Choo Park.
Application Number | 20060147615 11/370462 |
Document ID | / |
Family ID | 36640745 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060147615 |
Kind Code |
A1 |
Park; Byoung-Choo |
July 6, 2006 |
Organic semiconductor devices and organic electroluminescent
devices produced by using wet process
Abstract
The present invention provides a method for manufacturing an
organic semiconductor thin film by a wet process with a composite
solution prepared by dissolving at least two organic semiconductor
compounds in a mixed organic solvent including at least two organic
solvents having different volatility and having different
solubilities of the organic compounds at room temperature. Due to
the differences in the evaporation speeds of the solvents and the
solubilities of the organic compounds, the organic compounds are
continuously deposited according to the composition of solvent that
sequentially evaporates. Thus, the organic semiconductor thin film
having a continuous multi-layer (non-boundary multi-layer)
structure can be manufactured where different organic compounds
coexist between the organic layers. Especially, the composite
solution including at least two organic EL materials are used, and
the organic materials are controlled to deposit on the anode in the
order of hole injecting--hole transporting--light
emitting--electron transporting--electron injecting layers to form
an organic EL device.
Inventors: |
Park; Byoung-Choo;
(Kyonggi-do, KR) |
Correspondence
Address: |
ST. ONGE STEWARD JOHNSTON & REENS, LLC
986 BEDFORD STREET
STAMFORD
CT
06905-5619
US
|
Family ID: |
36640745 |
Appl. No.: |
11/370462 |
Filed: |
March 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10918872 |
Aug 16, 2004 |
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11370462 |
Mar 8, 2006 |
|
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PCT/KR03/00305 |
Feb 13, 2003 |
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10918872 |
Aug 16, 2004 |
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Current U.S.
Class: |
427/66 |
Current CPC
Class: |
H01L 51/5048 20130101;
H01L 51/0081 20130101; H01L 51/56 20130101; H01L 51/0042 20130101;
H01L 51/5012 20130101; H01L 51/0007 20130101; H01L 51/0059
20130101 |
Class at
Publication: |
427/066 |
International
Class: |
B05D 5/12 20060101
B05D005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2002 |
KR |
10-2002-0008269 |
Claims
1. A method for manufacturing an organic semiconductor device,
comprising the steps of: coating a composite solution on a
substrate, wherein the composite solution is prepared by dissolving
at least two organic compounds in a mixed organic solvent including
at least two organic solvents having different volatility and
having different solubilities of the organic compounds; and
continuously depositing the at least two organic compounds by
evaporating the organic solvents from the coated composite
solution.
2. The method of claim 1, wherein the organic compounds are at
least two organic compounds selected from the group consisting of
compounds for forming hole injecting layer, hole transporting
layer, light-emitting layer, electron transporting layer and
electron injecting layer, and the organic semiconductor device is
an organic light emitting device.
3. The method of claim 2, wherein the organic compounds further
include a dopant and/or a binder resin.
4. The method of claim 1, wherein the step for coating the
composite solution on the substrate is performed by a method
selected from the group consisting of a printing method, an inkjet
method, spin coating, and a dipping method.
5. The method of claim 1, further comprising the steps of: forming
an electrode after depositing the organic compounds; and
encapsulating the electrode and the deposited organic compounds
under an inert gas atmosphere.
6. The method of claim 1, wherein the organic solvents are selected
from the group consisting of methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl
alcohol, tert-butyl alcohol, dimethylformamide, dimethylacetamide,
ketone, acetone, diacetone alcohol, keto-alcohol, dioxane, ether,
polyethylene glycol, polypropylene glycol, polyalkylene glycol,
ethylene glycol, propylene glycol, butylene glycol, triethylene
glycol, hexylene glycol, diethylene glycol, glycerol,
ethyleneglycol monomethyl ether, diethyleneglycol methylether,
triethyleneglycol monomethylether, 2-pyrrolidon, toluene, xylene,
chlorobenzene, dichlorobenzene, chloroform, dichloromethane,
dichloroethane, gamma-butyl lactone, butyl cellosolve, cyclohexane,
NMP(N-methyl-2-pyrrolidon), cyclohexanone, tetrahydrofurane(THF),
carbon tetrachloride, tetrachloroethane, octylbenzene,
dodecylbenzene, quinoline, trichlorobenzene, nitrobenzaldehyde,
nitrobenzene, carbon disulfide, 2-heptanone, benzene, terpineol,
butylcarbitolacetate and ion exchange water.
7. The method of claim 1, wherein a concentration of the organic
compounds in the composite solution ranges from 0.005 to 10 wt
%.
8. The method of claim 1, wherein a viscosity of the composite
solution is less than 5000 cp.
9. The method of claim 1, wherein the organic semiconductor device
is an organic light emitting device, and the step for continuously
depositing the organic compounds is separately carried out for red,
green and blue pixels.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/918,872 filed on Aug. 16, 2004, which is a
continuation of International Patent Application No.
PCT/KR2003/000305 filed Feb. 13, 2003, which claims priority of
pending Korean Application No. 2002-8269, filed Feb. 15, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for manufacturing
an organic semiconductor thin film, and an organic semiconductor
device and an organic electroluminescent (EL) device manufactured
by the same, and more particularly to, a method for manufacturing
an organic semiconductor thin film by a wet process, and an organic
semiconductor device, such as an organic EL device, manufactured by
the same.
BACKGROUND OF THE INVENTION
[0003] Generally, organic semiconductor devices including organic
diode devices and organic transistor devices are based on the
electrical semi-conductivity that relates to the HOMO (Highest
Occupied Molecular Orbital) energy level and the LUMO (Lowest
Unoccupied Molecular Orbital) energy level of organic materials.
Examples of the organic diode devices include organic light
emitting diodes and organic electroluminescent (EL) diodes, and
examples of the organic transistor devices include organic FET
(Field Effect Transistors), organic TFT (Thin Film Transistors),
organic SIT (Static Induction Transistors), organic top gate SIT,
organic triodes, organic grid transistors, organic thyristors, and
organic bipolar transistors. In these organic semiconductor
devices, the electrical and optical properties of the devices are
strongly depending on the thin film structure of the organic layers
formed on a substrate. Thus, the development of the thin film
having an efficient structure is technically as important as the
development of new organic materials. The present invention relates
to a method for manufacturing an organic semiconductor thin film
having a new structure with high efficiency, and a device including
the organic semiconductor thin film. The present invention can be
widely applied to the above-mentioned various organic semiconductor
devices.
[0004] Hereinafter, the present invention will be described with
reference to the organic EL device, which has the simplest
structure among the above-mentioned devices. In the organic EL
device, a thin film including fluorescent organic compounds is
positioned between electrodes, cathode and anode. When a driving
voltage is applied to the organic EL device, electrons and holes
are injected into the LUMO and HOMO levels of the fluorescent
organic compound of the thin film from the cathode and anode,
respectively, and the injected electrons and holes are recombined
to produce excitons, which emit light (fluorescence or
phosphorescence) through losing their activity. In the present
invention, a light-emitting device represents an image display
device using the organic EL device. The light-emitting devices also
include the following modules: a module formed by mounting a
connector such as an anisotropic conductive film, FPC (Flexible
Printed Circuit), TAB (tape automated bonding) tape or TCP (Tape
Carrier Package) to the EL device, a module where a printed circuit
board is installed at the end of the TAB tape or TCP, and a module
formed by mounting an IC directly on the EL device by a method of
COG (chip on glass). Recently, a method for producing an organic or
inorganic semiconductor device on a substrate has been considerably
developed, and an active matrix display device (light-emitting
device) including the organic or inorganic semiconductor device has
been also being developed. In the present invention, the
semiconductor device also represents a single device or a plurality
of devices, which have a switching function.
[0005] The organic EL device (also referred as `EL display device`)
is a self light-emitting device, and can be produced as a simple
passive matrix light-emitting device or an active matrix
light-emitting device using TFT. In the organic EL device, organic
EL layers are positioned between electrodes, as shown in FIG. 1a.
As shown in the figure, the organic EL layers generally have a
multi-layered structure, in which the boundary or interface of each
layer is clearly distinguished. The representative example of the
multi-layer structure, suggested by Tang, et al., includes a hole
transporting layer 13, a light-emitting layer 14 and an electron
transporting layer 15 (Tang. C. et al. Appl. Phys. Lett. 1987, 51,
913-915). This structure shows high light-emitting efficiency and
thus the structure is adopted in almost all kinds of EL devices.
Another examples of the multi-layer structure include a structure
having a hole injecting layer 12, a hole transporting layer 13, a
light-emitting layer 14 and an electron transporting layer 15 which
are sequentially formed on an anode 11 of a substrate 10, and a
structure having a hole injecting layer 12, a hole transporting
layer 13, a light-emitting layer 14, an electron transporting layer
15 and an electron injecting layer 16 which are sequentially formed
on an anode 11 of a substrate 10 (See FIG. 1a). The light-emitting
layer 14 can be doped with fluorescent dopants. Besides the
monomeric low molecular weight EL material, conjugated polymers
such as poly(phenylvinylene) were introduced as the EL material in
1990 by Burroughes et al. (Burroughes, J. H. Nature 1990. 347.
539-541). Recently, stability, efficiency and durability of the
polymer EL material have been remarkably improved. In this
specification, all layers sandwiched between the electrodes are
called as the EL layers. Accordingly, the EL layer 20 includes the
hole injecting layer 12, the hole transporting layer 13, the
light-emitting layer 14, the electron transporting layer 15 and the
electron injecting layer 16. When a voltage is applied to the EL
layer 20 from the electrodes 11, 17, the electron-hole are
recombined at the light-emitting layer 14 to induce the
light-emission. In this specification, the EL device also
represents the light-emitting device including the electrodes 11,
17 and the EL layer 20. In order to prevent the EL device from
being deteriorated due to the exterior air, the substrate (EL
panel) on which the EL device has been formed is encapsulated with
a sealing material (packaging), and is bonded to a cover member.
Then, the connectors (FPC, TAB, etc.) are mounted for connecting
the encapsulated EL device to an external driving circuit, which
produces a passive or active matrix light-emitting device.
[0006] The EL layer 20 can be formed by various methods. Exemplary
methods include dry processes such as vacuum evaporation and
sputtering, and wet processes such as spin coating, a cast method,
an inkjet method, a dipping method, and a printing method. Besides,
roll coating, an LB method and ion plating method can also be used.
In case of using a low molecular weight compound having a good
thermal stability and capable of being sublimated to form a thin
film, the dry process such as vacuum evaporation is generally used
to manufacture the multi-layer EL device shown in FIG. 1a. However,
the dry process requires a high vacuum environment, the
manufacturing conditions should be controlled carefully, and thus
the process for fabricating EL devices is complex, resulting in the
large manufacturing costs. On the contrary, the wet process, which
uses a solution of the organic compounds dissolved in a solvent,
and forms an organic layer of the dissolved compounds, has an
advantage in that the EL layer can be easily formed. Moreover, the
wet process can be used not only for the low molecular weight
compound but also for the organic polymer materials. On the other
hand, there are disadvantages in the wet process, because of the
solvent problem for forming multi-layer structure. Namely,
different solvent must be used to form each different layer in
forming the multi-EL layer. In this case, to form an upper organic
layer on the lower organic layer, a solution, which does not
dissolve the lower organic layer formed previously on the
substrate, must be used to form the multi-EL layer. However, it is
generally difficult to select appropriate set of the solvents to
form the multi-EL layers. If an improper solvent is used, the
organic layer previously formed on the substrate 10 may be
re-dissolved by the solvent to form a new upper layer, and some of
the organic materials of the lower or upper organic layers may
irregularly diffuses into the neighboring layers. Thus, it is
difficult to manufacture the multi-EL layers 20 of FIG. 1a by
simply repeating the conventional wet process. Therefore, as shown
in FIG. 1b, the wet process is generally carried out to form a
single-EL layer 20 in which one or more compounds are uniformly
dispersed in the single-EL layer 20. As a result, the EL device
manufactured by the conventional wet process shows the low
light-emitting efficiency and requires high driving voltage. In
some cases, the multi-EL layer 20 can be formed by combination of
the wet process and the dry process. However, the multi-EL layer 20
produced with this method also has the low light-emitting
efficiency and requires high driving voltage.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a method
for solving the foregoing problems of an organic semiconductor thin
film, such as an organic EL thin film manufactured by the
conventional wet process. Another object of the present invention
is to provide an organic semiconductor device, which can be easily
manufactured and have improved operation reliability. Yet another
object of the present invention is to provide an organic EL device
having improved quality of display images. Yet another object of
the present invention is to provide an economical and efficient EL
display device produced with reduced costs.
[0008] In order to achieve these objects, it is provided a method
for manufacturing an organic semiconductor thin film by a wet
process, which uses a composite solution prepared by dissolving at
least two organic semiconductor materials in a mixed solvent
including at least two organic solvents having different volatility
and having different solubilities of the organic semiconductor
materials at room temperature, and an organic semiconductor device
manufactured by the same. If the organic semiconductor device is an
organic EL device, the organic semiconductor materials include
organic compounds having electrical and optical properties for
injecting or transporting hole, light-emitting, and transporting
and injecting electron et. al.
[0009] When the composite solution is used to form a device on a
substrate by a printing method, an inkjet method, spin coating or a
dipping method, the solvents of the composite solution are
sequentially evaporated due to the differences of volatility, and
the organic materials having the lower solubility to the residual
solvents are sequentially deposited onto the substrate due to the
differences of solubility. Therefore, the organic layers are
sequentially deposited in the form of a continuous multi-layer
structure having indistinct boundaries. Here, each organic layer
may include a small amount of a different kind of organic materials
of the neighboring organic layers, and the continuous boundary
region between the neighboring organic layers includes at least two
kinds of materials of the neighboring organic layers in mixed form.
Namely, the organic semiconductor layers of the present invention
is formed so that the concentrations of at least two organic
semiconductor materials (compounds) change with a gradient along
with their deposition direction at the interface. The thin film of
the present invention forms a continuous multi-layer structure,
which is different from the simple conventional multi-layer thin
film (FIG. 1a) or uniformly distributed single-layer thin film
(FIG. 1b).
[0010] It is also provided a method for manufacturing an EL layer
having a continuous multi-layer structure by using a composite
solution designed to sequentially deposit a hole injecting
material, hole transporting material, light-emitting material,
electron transporting material, and electron injecting materials on
an anode. It is known that a single or simply mixed organic solvent
can be used in the wet process for manufacturing the EL thin film.
For example, Korean Patent Publication Nos. 2001-0110183,
2001-0078227 and 2000-0062303 disclose that the EL layer can be
formed by dissolving EL material in a single or mixed solvent.
However, any of them does not suggest the method for forming the
continuous and non-boundary multi-layer structure which is provided
by the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1a is a structure diagram for illustrating the
conventional organic EL device having a multi-layer structure;
[0012] FIG. 1b is a structure diagram for illustrating the
conventional organic EL device having a uniformly dispersed
single-layer structure;
[0013] FIG. 2a is a structure diagram for illustrating an organic
EL device having a continuous non-boundary multi-layer organic
semiconductor thin film in accordance with the first embodiment of
the present invention;
[0014] FIG. 2b is a structure diagram for illustrating an organic
EL device having a continuous non-boundary multi-layer organic
semiconductor thin film in accordance with the second embodiment of
the present invention;
[0015] FIGS. 3a and 3b are graphs showing V-I and V-L
characteristics of the EL device in accordance with the first
embodiment of the present invention;
[0016] FIGS. 4a and 4b are graphs showing V-I and V-L
characteristics of the EL device in accordance with the second
embodiment of the present invention;
[0017] FIGS. 5a and 5b are graphs showing V-I and V-L
characteristics of an EL device in accordance with the comparative
example 1; and
[0018] FIGS. 6a and 6b are graphs showing V-I and V-L
characteristics of an EL device in accordance with the comparative
example 2.
DETAILED DESCRIPTION OF THE INVENTION
[0019] An organic semiconductor device and an organic EL device
manufactured by a wet process in accordance with the present
invention will now be described in detail with reference to the
accompanying drawings. In the following description, same reference
numerals are used for the same elements even in different
drawings.
[0020] In the EL device of the present invention, the continuous
non-boundary multi-layer structure of an organic semiconductor thin
film includes at least two layers. For example, it may have one of
the following structures. Here, ".about." means the continuous
non-boundary interface, while "/" means the distinct interface.
[0021] (1) anode/hole injecting, transporting
layers.about.light-emitting layer/cathode
[0022] (2) anode/light-emitting layer.about.electron transporting,
injecting layers/cathode
[0023] (3) anode/hole injecting, transporting
layers--light-emitting layer.about.electron transporting, injecting
layers/cathode.
[0024] The organic semiconductor thin film suggested by the present
invention can be forced to be formed by depositing compounds in the
order of hole injecting layer, hole transporting layer,
light-emitting layer, electron transporting layer and electron
injecting layer on the anode. The thickness of the organic
semiconductor thin film ranges from 0.001 to 1 .mu.m, which is not
intended to be limiting. FIG. 2a shows the representative example
of the organic EL device of the present invention. As shown in FIG.
2a, the organic EL device includes an organic semiconductor thin
film, namely an EL layer 20 formed by sequentially depositing at
least two organic semiconductor materials (compounds) between
electrodes 11, 17. The organic semiconductor materials form a hole
injecting layer 12, a hole transporting layer 13, a light-emitting
layer 14, an electron transporting layer 15 or an electron
injecting layer 16, and the concentration of the material changes
with a gradient along with its deposition direction at the
interfaces. In addition, as shown in FIG. 2b, a hole injecting
layer 12, a hole transporting layer 13, a light-emitting layer 14
and an electron transporting layer 15 can be produced to a
continuous non-boundary multi-layer structure, and an electron
injecting layer 16 can be formed by a conventional wet process or a
dry process such as vacuum evaporation on the non-boundary
multi-layer.
[0025] In the present invention, the vacuum evaporator to form an
organic multi-layer is not necessary, thus the whole manufacturing
system can be simplified and easily maintained. In addition, the
present invention can be applied to an active matrix EL device as
well as a passive matrix EL device.
[0026] The organic EL device of the present invention can be
manufactured by coating a composite solution prepared by dissolving
at least two organic compounds in a mixed solvent including at
least two organic solvents having different volatility and having
different solubilities of the organic compounds, on the substrate
where the electrode has been formed, and by evaporating the organic
solvents from the coated composite solution to sequentially deposit
the organic compounds. The composite solutions used to produce the
organic EL device may include at least one organic light-emitting
semiconductor compound emitting red, green or blue light.
Preferably, the composite solution is optimized to enable the
devices to display wide ranges of colors (for example, 460, 520 and
650 nm of narrow lines for B, G and R). The light-emitting
materials of the organic EL device of the present invention are not
limitative, and thus a variety of the conventional compounds for
manufacturing an organic EL device can be used in the present
invention. Preferably, low molecular weight fluorescent materials
or fluorescent polymer materials having the light-emitting property
can be used, and the mixture of the low molecular weight materials
and the polymer materials can also be used.
[0027] Exemplary low molecular weight organic compounds used as the
green light-emitting materials include Alq.sub.3, BeBq.sub.2
(10-benzo[h]quinolinol-beryllium complex), and Almq
(tris(4-methyl-8-quinolinolate)aluminum) which emit light in a
green color range (550 nm). Typically, a few mol % of quinacridone,
coumarin, C545T (Eastman Kodak Co.), or Ir-complex can be added
(doped) to improve light-emitting efficiency and durability. Also,
exemplary doping materials of a red light-emitting layer include
Indigo, Nile Red, DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethyl
aminostyryl)-4H-pyran), DCJTB (Eastman Kodak Co.), and Pt-complex.
Exemplary blue light-emitting materials include metal complexes
such as ZnPBO ((Bis[2-(2-benzoxazolyl)phenolato]Zinc(II)) and Balq
(Bis(2-methyl-8-quinolinolato) (para-phenyl-phenolato) aluminum),
or non-metal complexes such as styrylarylene derivatives, namely
DPVBi (4,4'-bis(2,2'-biphenylvinyl)-1,1'-biphenyl), oxadiazole
derivatives, bisstyryl anthracene derivatives, and bisstyryl
arylene derivatives such as BczVBi
(4,4'-Bis((2-carbazole)vinylene)biphenyl). However, the
light-emitting materials of the organic EL device of the present
invention are not specifically limited, and thus the aforementioned
materials are not intended to be limiting. Exemplary polymer
organic compounds, used as the light-emitting materials of the
organic EL device, include poly(p-phenylene),
polyphenylene-vinylene, polyarylene, polyalkylthiophene and
polyalkylfluorine. When the fluorescent polymer materials are used
for the light-emitting layer of the organic EL device, the
fluorescent polymer materials can be a block, random or graft
copolymers, which also are not intended to limiting the present
invention.
[0028] In the organic EL device of the present invention, exemplary
hole injecting and hole transporting materials include soluble
phthalocyanine compounds, aromatic diamine compounds such as TPD
((N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine:
triphenylamine derivative), MTDATA (4,4',4'-tris[3-methylphenyl
(phenyl)amino]triphenylamine), quinacridone, bisstyryl anthracene
derivatives, PVK(polyvinyl carbazole), porphyrinic compounds,
.alpha.-NPD
(N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine),
polyaniline, and conductive polymers, which is not intended to be
limiting. Exemplary electron injecting and electron transporting
materials include Alq.sub.3 which is an aluminum complex prepared
by coordinating three hydroxyquinolines on aluminum atoms, and
distyrylbiphenyl derivatives, which is not intended to be
limiting.
[0029] In the organic EL device of the present invention, the
light-emitting layer and other organic layers can be formed to a
thin film with an appropriate binder resin. If necessary, an
appropriate dopant can be included in the layer. Exemplary binder
resins include polyvinylcarbazole(PVK) resins, polycarbonate
resins, polyester resins, polyallylate resins, butyral resins,
polyvinylacetal resins, diallyphthalate resins, acrylic resins,
methacrylic resins, phenol resins, epoxy resins, silicone resins,
polysulfone resins and urea resins. The resins can be used alone or
as a copolymer including two or more resins, which is not intended
to be limiting.
[0030] Exemplary solvents for forming the mixed solvent of the
present invention include methyl alcohol, ethyl alcohol, n-propyl
alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,
tert-butyl alcohol, dimethylformamide, dimethylacetamide, ketone,
acetone, diacetone alcohol, keto-alcohol, dioxane, ether,
polyethylene glycol, polypropylene glycol, polyalkylene glycol,
ethylene glycol, propylene glycol, butylene glycol, triethylene
glycol, hexylene glycol, diethylene glycol, glycerol,
ethyleneglycol monomethyl ether, diethyleneglycol methylether,
triethyleneglycol monomethylether, 2-pyrrolidon, toluene, xylene,
chlorobenzene, dichlorobenzene, chloroform, dichloromethane,
dichloroethane, gamma-butyl lactone, butyl cellosolve, cyclohexane,
NMP(N-methyl-2-pyrrolidon), cyclohexanone, tetrahydrofurane(THF),
carbon tetrachloride, tetrachloroethane, octylbenzene,
dodecylbenzene, quinoline, trichlorobenzene, nitrobenzaldehyde,
nitrobenzene, carbon disulfide, 2-heptanone, benzene, terpineol,
butylcarbitolacetate and ion exchange water (pure water). The
above-mentioned solvents are typical examples of the solvents which
can be used in the present invention, and the present invention is
not limited to the listed solvents. In the present invention, the
selection of the at least two organic solvents having different
volatilities may depend on the property of the organic compounds.
Generally, organic solvents having boiling point difference more
than 3.degree. C., preferably 5.degree. C., more preferably
10.degree. C. can be used. If the difference in volatilities of the
organic solvents is too small, the evaporation of the organic
solvents must be slowly carried out. Otherwise, the organic
compounds may not be deposited sequentially. In addition, the
organic solvents are selected to sequentially deposit the organic
compounds due to the organic compounds' solubility difference. If
the solubilities of the organic compounds with respect to the
selected solvents are the same, it is impossible to form the
organic thin film having a concentration gradient according to the
present invention.
[0031] The viscosity of the composite solution may affect the
thickness of the EL layer, and the thickness of the EL layer is
controlled to optimize the emitting intensity. The viscosity of the
composite solution can be adjusted by the selection of solvents,
preferably less than 5000 cp. The lower limit of the viscosity is
not important in the present invention, but for example more than
100 cp, more preferably more than 1000 cp. The concentration of the
EL materials in the solvents is determined so as to be suitable for
the wet process, preferably from 0.005 to 10 wt %, more preferably
0.01 to 10 wt %. If the viscosity and concentration are away from
the above ranges, the film formation by the wet process may not be
efficiently performed.
[0032] When the EL layer 20 is formed by using the composite
solution according to the wet process such as the spin coating,
cast method, inkjet method, dipping method and printing method, the
EL layer 20 may be deteriorated due to the moisture and oxygen of
air. In order to remove moisture and oxygen, the EL layer 20 is
preferably manufactured with a film formation device installed in a
booth filled with low reactive gases, for example rare gases or
inert gases such as argon, helium and nitrogen. Thereafter, the
solvents to form the EL layer 20 are sequentially and completely
removed by thermal evaporation. Preferably, the solvents are
evaporated at a temperature lower than a glass transition
temperature of the EL materials. In addition, the EL layer 20 can
be formed with polymer precursors, and then the precursors can be
transformed into polymer EL materials by heating or UV curing.
[0033] Then, the cathode 17 (or anode 11) is formed on the EL layer
20 formed on the anode 11 (or cathode 17) of the substrate 10. In
general, the anode 11 is preferably made of a material having a
high work function. Exemplary anode 11 materials include silver,
nickel, gold, platinum, palladium, selenium, rhenium, iridium,
alloys thereof, tin oxide, indium-tin-oxide, and copper iodide. In
addition, conductive polymers such as polyaniline,
poly(3-methylthiophene), polyphenylene sulfide and polypyrrole can
be the materials for forming the anode. On the contrary, the
cathode 17 is preferably made of a material having a low work
function. Exemplary cathode materials include Al, Mg, Li, Cs, Ba,
K, Be or Ca. Also, an electrode including MgAg (Mg: Ag=10:1) is
preferably used, and MgAgAl electrode, LiAl electrode and LiF/Al
electrode can be used. Optionally, a protective electrode to
protect the cathode from external moisture can be formed, and the
materials including Al or Ag can be used as the protective
electrode.
[0034] Examples of the substrate 10 on which the EL layer 20 and
the electrodes 11, 17 are formed include a transparent substrates
made of glass, quartz or polymer and inorganic semiconductor
substrates made of silicon or gallium arsenide, which is not
intended to be limiting the present invention. Finally, in order to
protect the EL device from external oxygen and moisture, the EL
device is encapsulated with a sealing member such as glass,
ceramic, plastic and metal under the inert gas atmosphere, or
encapsulated with a thermosetting resin or ultraviolet ray curable
resin. In addition, it is preferable to insert a hygroscopic
material in the encapsulated space, and the representative example
of the hygroscopic material is barium oxide.
[0035] In this specification, the device having one pixel is mainly
disclosed to illustrate the present invention. However, a plurality
of pixels having the same structure can be aligned in a matrix type
to form the device of the present invention, and the color EL
display device can also be manufactured according to the present
invention. In addition, the present invention also can be applied
to the color display devices in which a white EL device and a color
filter are combined, a blue or bluish green EL device and a
fluorescent color covering material layer are combined, or a
transparent electrode is used as a cathode and an EL device
corresponding to RGB is respectively laminated. It is also possible
to manufacture a black and white display device by forming a white
light-emitting layer on an EL layer. Example of the active matrix
organic EL display according to the present invention includes a
thin film transistor switching device. However, the present
invention is not limited thereto, and other switching devices, such
as two terminal devices, for example, MIM can also be used.
Moreover, passive driving, static driving and segment display
driving can also be used in the present invention. In addition, a
single or plurality of switching devices can be formed on one
pixel.
[0036] The organic EL device of the present invention will be
better understood by referring to the following examples:
EXAMPLE 1
[0037] In this example, low molecular weight compound and polymer
material were used as the organic semiconductor EL materials. PVK
(poly-N-vinylcarbazole, molecular weight: 150,000,
T.sub.mp=277.degree. C., T.sub.g=156.degree. C.) was used as the
charge carrier binder resin, .alpha.-NPD (4,4
bis[N-(1-napthyl-N-phenyl-amino)biphenyl]) was used as the hole
transporting material, and green light emitting Alq.sub.3
(tris(8-quinolinolato)aluminum) was used as the light-emitting
material and the electron transporting material. 1:1 (weight ratio)
mixture of chloroform and dichloroethane (ClCH.sub.2CH.sub.2Cl) was
used as the mixed solvent. Here, the boiling points of chloroform
and dichloroethane were 62.degree. C. and 82.degree. C.,
respectively. Firstly, in order to evaluate the depositing speed
and depositing order of each organic material in the mixed solvent,
the EL materials were dissolved in the mixed solvent in the amount
of 0.05 wt %. The depositing order of the EL materials according to
the evaporation of the mixed solvent was evaluated. As the
evaporation proceeded, chloroform was firstly evaporated, and
.alpha.-NPD and PVK having lower solubilities in the dichloroethane
were deposited to form a thin film. At the same time, a small
amount of Alq.sub.3 was also co-deposited. When chloroform was
almost completely evaporated, deposition of .alpha.-NPD was ceased.
Then, dichloroethane was evaporated, and Alq.sub.3 dissolved in the
solution (dichloroethane) was deposited with PVK to form another
thin film on the lower .alpha.-NPD and PVK layer. On the boundary
between the .alpha.-NPD and Alq.sub.3 thin films, .alpha.-NPD and
Alq.sub.3 are coexisted, and PVK was evenly dispersed on the whole
thickness range of the thin films. Therefore, the mixed solution
was useful for depositing the continuous non-boundary
.alpha.-NPD.about.Alq.sub.3 multi-layer ((1) anode/hole injecting
and transporting layers.about.light-emitting layer/cathode), and
PVK worked as the charge carrier binder resin.
[0038] The EL device according to an embodiment of the present
invention was formed as follows. An organic EL layer was made of an
organic semiconductor thin film formed by continuous depositions
thereof.
[0039] (a) A glass substrate coated with Indium-Tin-Oxide (ITO) was
ultrasonically washed in a commercially available cleaning agent,
and then washed with deionized water.
[0040] (b) The composite solution (chloroform:dichloroethane=1:1),
in which PVK, .alpha.-NPD and Alq.sub.3 organic materials were
dissolved, was filtered through 0.2 .mu.m Teflon filter.
Thereafter, the composite solution was spin-coated on the ITO for 3
minutes under a spinning speed of 3000 rpm.
[0041] (c) The EL layer was thermally treated at 80.degree. C. for
30 minutes to completely evaporate the solvents in the EL layer.
The thickness of the produced thin film was 500 to 700 .ANG..
[0042] (d) 2000 .ANG. of Al:Li cathode was deposited on the EL
layer with vacuum evaporation. The degree of vacuum was
5.times.10.sup.-6 torr, and the deposition speed was 10
.ANG./second. Thereby, a circular shape organic EL device having a
diameter of 4 mm was obtained. In order to protect the EL device
from the external environment, the EL device was encapsulated in a
dry globe box.
[0043] The produced
(ITO/.alpha.-NPD(PVK).about.Alq.sub.3(PVK)/Al:Li) EL device had the
light-emitting initiation voltage (Vonset) of .about.13V, and the
current flowing through the EL device and the EL intensity at the
voltage of 20V were 3.5 mA and .about.196 cd/m.sup.2, respectively.
The EL device emitted the uniform green light (540 nm). In
addition, when the device was driven at a constant voltage of 20V,
the organic EL display panel performed the stable light emission
for a long time. The characteristics of the EL device are
summarized in Table 1, and the voltage-current (V-I) and voltage-EL
intensity (V-L) properties of the EL device are shown in FIGS. 3a
and 3b, respectively.
EXAMPLE 2
[0044] The same organic materials as the EL materials of Example 1
were used in this Example. 1:1 (weight ratio) mixture of
dichloroethane and dichloromethane (CH.sub.2Cl.sub.2) was used as
the mixed solvent. Here, the boiling points of dichloroethane and
dichloromethane were 82.degree. C. and 40.degree. C., respectively.
The deposition speed and deposition order of each organic material
from the mixed solvent were evaluated.
[0045] As the evaporation proceeded, dichloromethane was firstly
evaporated, and .alpha.-NPD and PVK having lower solubilities in
dichloroethane were deposited to form a thin film. At the same
time, a small amount of Alq.sub.3 was also deposited. When
dichloromethane was almost completely evaporated, deposition of
.alpha.-NPD was ceased. Then, dichloroethane was evaporated, and
Alq.sub.3 dissolved in the solution (dichloroethane) was deposited
with PVK to form another thin film on the lower .alpha.-NPD and PVK
layer. On the boundary between the .alpha.-NPD and Alq.sub.3 thin
films, .alpha.-NPD and Alq.sub.3 are coexisted, and PVK was evenly
dispersed on the whole thickness range of the thin films.
Therefore, the mixed solution was useful for depositing the
continuous non-boundary .alpha.-NPD.about.Alq.sub.3 multi-layer,
and PVK worked as the charge carrier binder resin.
[0046] The EL device according to an embodiment of the present
invention was formed according to the method described in Example 1
except for using the mixed solvent
(dichloroethane:dichloromethane=1:1). The produced EL device had
the light-emitting initiation voltage (V.sub.onset) of .about.13V,
and the current flowing through the EL device and the EL intensity
at the voltage of 20V were 2.9 mA and .about.210 cd/m.sup.2,
respectively. The EL device emitted the uniform green light (540
nm). In addition, when the device was driven at a constant voltage
of 20V, the organic EL display panel performed the stable light
emission for a long time. The characteristics of the EL device are
summarized in Table 1, and the voltage-current (V-I) and voltage-EL
intensity (V-L) properties of the EL device are shown in FIGS. 4a
and 4b, respectively.
COMPARATIVE EXAMPLE 1
[0047] The same organic materials as the EL materials of Example 1
were used in this Comparative Example. 1:1 (weight ratio) mixture
of chloroform and toluene was used as the mixed solvent. Here, the
boiling points of chloroform and toluene were 62.degree. C. and
110.degree. C., respectively. The deposition speed and deposition
order of each organic material from the mixed solvent were
evaluated. As the evaporation proceeded, chloroform was firstly
evaporated, and Alq.sub.3, .alpha.-NPD and PVK having lower
solubilities to toluene were deposited to form a non-uniform thin
film. When chloroform was completely evaporated, the depositions of
Alq.sub.3 and .alpha.-NPD were ceased. Then, toluene was
evaporated, and PVK dissolved in the solution was deposited to form
a uniform thin film. Thus, the mixed solvent was not useful for
forming the continuous non-boundary multi-layer.
[0048] The EL device was formed according to the method described
in Example 1 except for using the mixed solvent
(chloroform:toluene=1:1). The produced EL device had the
light-emitting initiation voltage (V.sub.onset) of .about.18V, and
the current flowing through the EL device and the EL intensity at
the voltage of 20V were less than 0.3 mA and .about.1 cd/m.sup.2
respectively. The EL device emitted the non-uniform and unstable
green light. The characteristics of the EL device are summarized in
Table 1, and the voltage-current (V-I) and voltage-EL intensity
(V-L) properties of the EL device are shown in FIGS. 5a and 5b,
respectively.
COMPARATIVE EXAMPLE 2
[0049] The same organic materials as the EL materials of Example 1
were used in this Comparative Example. The single solvent of
chloroform was used as the solvent. The deposition order of each
organic material from the solvent was evaluated. As the chloroform
evaporated, Alq.sub.3, .alpha.-NPD and PVK were deposited to form a
uniform thin film. Thus, the single solvent was useful for forming
the single-layer where .alpha.-NPD and Alq.sub.3 were uniformly
dispersed, but was not useful for forming the continuous
non-boundary multi-layer.
[0050] The EL device was formed according to the method described
in Example 1 except for using the single solvent (chloroform). The
produced organic thin film was a single layer in which the organic
materials are uniformly dispersed. The produced EL device had the
light-emitting initiation voltage (V.sub.onset) of .about.19V, and
the current flowing through the EL device and the EL intensity at
the voltage of 20V were less than 0.5 mA and .about.1 cd/m.sup.2
respectively. The EL device emitted the non-uniform and unstable
green light. The characteristics of the EL device are summarized in
Table 1, and the voltage-current (V-I) and voltage-EL intensity
(V-L) properties of the EL device are shown in FIGS. 6a and 6b,
respectively.
[0051] Therefore, the EL device having the organic semiconductor
thin film with continuous non-boundary multi-layer structure of
Examples 1 and 2 have much better operation efficiency than the EL
device having single layer thin film of Comparative Examples 1 and
2. The properties of the produced EL devices are summarized in
Table 1. TABLE-US-00001 TABLE 1 Shape of V.sub.onset EL intensity
Current at thin film (V) at 20 V 20 V (mA) Example 1 Non-boundary
13.0 195.6 3.5 multi-layer Example 2 Non-boundary 13.0 209.5 2.9
multi-layer Comparative Uniformly 18.0 0.6 0.3 Example 1
distributed multi layer Comparative Uniformly 19.0 0.8 0.5 Example
2 distributed layer
[0052] As described, the organic semiconductor thin film having the
non-boundary multi-layer structure of the present invention is
different from the conventional uniformly distributed single-layer
film or multi-layer film, and can be easily manufactured. The
organic EL device has the lower driving voltage and higher
operation efficiency than the devices produced with the single or
simply mixed solvents. Thus, it is possible to reduce the
manufacturing cost of the efficient light-emitting device and
produce an electronic device having high quality of display images.
The organic EL device of the present invention can be applied to
various display devices, televisions, digital cameras, computers,
notebook computers, mobile computers, portable image recording or
displaying device, screens, bulletin boards, store signs, goggle
type displays, car displays, video cameras, printer displays,
remote control devices, phone displays, mobile phones, etc.
[0053] As shown in the above Examples, the organic semiconductor
thin film of the present invention having the non-boundary
multi-layer structure has the excellent "applied voltage": "light
emitting intensity" property, and "applied voltage": "current"
properties, which are similar to non-linear current properties of a
typical diode device. As a result, the organic semiconductor thin
film of the present invention can also be applied to various
organic semiconductor devices such as organic diode devices.
[0054] While the present invention has been shown and described
with reference to certain preferred embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *